<template>
  <div class="list">
    <div class="item" 
    v-for="item of letters" :key="item"
    :ref="item"
    @touchstart.prevent="handleTouchStart"
    @touchmove="handleTouchMove"
    @touchend="handleTouchEnd"
    @click="handleLetterClick"
    >{{item}}</div>
  </div>
</template>

<script>
export default {
  name: 'CityAlphabet',
  data(){
  return{
    touchStatus:false,
    startY: 0,
    timer: null
  }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  props:{
    cities:Object
  },
  computed:{
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  methods:{
    handleLetterClick(e){
      // console.log(e.target.innerHTML);
      this.$emit('change',e.target.innerHTML)
      // 提交给父组件,父组件接收后传递给兄弟组件
    },
    handleTouchStart(){
      this.touchStatus= true
    },
    handleTouchMove(e){
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd(){
      this.touchStatus = false
    },
  }
}
</script>

<style lang="stylus" scoped>
  @import '~@/assets/style/varibles.styl';
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
